Did Nick Clegg really come out well from the debate? Photograph: Getty Images

The consensus that Nick Clegg won the first leadership debate is proof that a substantial number of voters in post-debate polls just weren't paying attention – that, or they made up their minds for non-debate reasons. You've won a debate, I think, if you're better than everyone else at presenting and backing up your case; and at going after your opponents when they try to make theirs. Lib Dem leader Nick Clegg didn't just not win any of those categories: he failed to excel in any; was positively dismal at actually backing up his serious positive case or making serious trouble for the opposition; and did reasonably well only with his presentation.

Two of the memorable examples. Clegg argued that Labour immigration policy hadn't been stringent enough – he wanted to remedy this by adding a further criterion on entry visas to the UK which would mean that, in addition to present conditions (sponsor, job to go to), immigrants entering the country to work would be tied to specific regions. Cameron quite sensibly laughed off the point: companies are hardly going to make effective guardians of internal borders. Clegg's comeback was pure waffle: regionalisation has worked elsewhere, and we should expect it to work here. Cameron could barely stop smirking; the headlines this morning must burn. If Clegg can get away with setting out this waffly policy – the implementation of which he can't detail, and the authoritarianism of which severely dents the Lib Dems' civil liberties brand – what can't he get away with?

Things initially looked better when it came to Trident. Clegg boldly made the case for unilateral renunciation. I'll admit to not having realised that more than £100bn would be committed to Trident – I half-remembered reading that it would cost £20bn, so went online, only to discover that the higher figure checks out. Score one for Clegg. The only other reason advanced for giving it up was that it was designed for cold war realities. But even as a soundbite, this sounded unserious. Both Cameron and Brown made sensible replies about the security costs of giving up the deterrent; Clegg devolved into mantras about the end of the cold war. It was at least open to him to simply argue the point that the security gained isn't worth the £100bn – he didn't. He had a creative, relatively popular piece of policy which, if presented well, could have made life difficult for the other two, but he botched the presentation, as well as the rebuttals. Unimpressive, but maybe in keeping with Lib Dem tradition.